1. Field of the Invention
This invention relates to a two-wheel drive and four-wheel drive change-over apparatus suitably used for a part-time four-wheel drive vehicle (4WD) and the like, and an actuator for driving the same.
2. Related Art
A part-time four-wheel drive vehicle (4WD) capable of driving four wheels only in case of necessity in a two-wheel drive vehicle is known. A change-over apparatus for switching two-wheel driving condition and four-wheel driving condition from one to the other in such a part-time four-wheel drive vehicle is also known which is adapted to selectively drive a two-wheel drive and four-wheel drive change-over shaft and a four-wheel speed change-over shaft so that four driving condition including two-wheel driving, four-wheel high-speed driving, four-wheel neutral and four-wheel low-speed driving condition can be switched from one to another.
A related art actuator has some inconveniences. Namely, when two-wheel driving condition is switched to four-wheel driving condition, the phases of an output gear for rear wheels and a front drive gear are shifted from each other, and the spline engaging of the two gears with each other cannot be done by a two-wheel and four-wheel drive change-over slider in some cases. When four-wheel driving condition is switched to two-wheel driving condition, the power needed to stop the spline engaged condition of the two gears becomes too large, and the two gears cannot be disengaged from each other in some cases. It is also known that this actuator is provided as countermeasures with a waiting mechanism for waiting for a certain period of time until the time at which the two gears are meshed with each other or disengaged from each other. The related art examples of such techniques include the techniques disclosed in, for example, JP-A-7-179138. A waiting mechanism disclosed in this publication includes a spiral spring, first and second plates and a bush member. Therefore, the number of the parts is large, and a work efficiency in the assembling of the parts is low. Moreover, since the dimensions of the waiting mechanism increase, the actuator as a whole became large-sized.
Under the circumstances, the present invention has been made so as to solve these problems, and aims at providing a miniaturized, inexpensive actuator by reducing the number of parts constituting a waiting mechanism and thereby improving the work efficiency in the assembling of the parts.
A first invention provides an actuator which has two driven shafts arranged in parallel with each other and made movable in the axial direction thereof, and cams held on these driven shafts for driving the driven shafts respectively, and which is adapted to move the driven shafts selectively in the axial direction thereof by a predetermined stroke by driving each cam to a predetermined stopping position in accordance with a mode changed over from another by a switching operation of an operating switch having a plurality of modes to be switched, the actuator including a motor adapted to be rotated forward or backward by a current supplied thereto, a driving gear meshed with a worm formed on a shaft of the motor, an output shaft connected to the driving gear, a pair of cam followers adapted to be turned by a rotation of the output shaft, and engaged with the cams and drive the same, urging members held in urging member housings formed at predetermined intervals along a circle which is the same as an outer circumference of the driving gear, a rotation retaining plate mounted on the output shaft so that the rotation retaining plate cannot be rotated relatively thereto, a plurality of pressing parts each of which is formed so as to project from the rotation retaining plate, and each of which is capable of pressing either one of both end portions of each urging member, slits formed in the portions of the driving gear which are among the urging member housings so as to prevent the driving gear and pressing parts from interfering with each other, a first actuator case in which the driving gear, rotation retaining plate and output shaft are housed, and a second actuator case fixed to the first actuator case, supporting each driven shaft so that the driven shafts can be moved freely in the axial direction thereof and housing each of the cams therein, a rotation of the driving gear being transmitted to the output shaft via each urging member and rotation retaining plate, either one of both end portions of each urging member being pressed by a corresponding pressing part of the rotation retaining plate when the rotation of the driving gear is continued after the output shaft is locked and stopped in the intermediate position of the rotation thereof.
A second invention provides an actuator which is in accordance with that of the first invention, in which the plural urging member housings formed on the driving gear is three arcuate urging member housings arranged at regular intervals in the circumferential direction thereof, the urging members being three cylindrical compression springs.
A third invention provides an actuator for actuating a two-wheel drive and four-wheel drive change-over apparatus having a first change-over shaft for switching two-wheel drive/four-wheel drive and a second change-over shaft for changing speeds of four wheels, the first and second change-over shaft being arranged in parallel with each other in a transfer and movable in axial directions thereof by cams held on the first and second change-over shafts for driving the first and second change-over shafts respectively, wherein the actuator is adapted to switch selectively from one to another of four driving conditions including two-wheel drive, four-wheel high-speed drive, four-wheel neutral and four-wheel low-speed driving condition by driving the cams in the change-over apparatus to predetermined stopping positions respectively in accordance with a mode changed by a shifting operation of a mode change-over switch, and thereby moving the change-over shafts selectively in the axial directions at predetermined strokes, the actuator including: a motor adapted to be rotated forward or backward by a current supplied thereto, a driving gear meshed with a worm formed on a shaft of the motor, an output shaft connected to the driving gear, a pair of cam followers adapted to be turned by a rotation of the output shaft, and engaged with the cams and drive the same, urging members held in urging member housings formed at predetermined intervals along a circle which is the same as the outer circumference of the driving gear and in the circumferential direction thereof, a rotation retaining plate mounted on the output shaft so that the rotation retaining plate cannot be rotated relatively thereto, a plurality of pressing parts each of which is formed so as to project from the rotation retaining plate, and each of which is capable of pressing either one of both end portions of each urging member, slits formed in the portions of the driving gear which are among the urging member housings so as to prevent the driving gear and pressing parts from interfering with each other, a first actuator case in which the driving gear, rotation retaining plate and output shaft are housed, and a second actuator case fixed to the first actuator case, supporting each driven shafts so that the driven shafts can be moved freely in the axial direction and housing each of the cams therein, a rotation of the driving gear being transmitted to the output shaft via each urging member and rotation retaining plate, either one of both end portions of each urging member being pressed by a corresponding pressing part of the rotation retaining plate when the rotation of the driving gear is continued after the output shaft is locked and stopped in the intermediate position of the rotation thereof.
A fourth invention provides an actuator for driving a two-wheel drive and four-wheel drive change-over apparatus, which actuator is in accordance with that of the third invention, in which the plural urging member housings formed on the driving gear are three arcuate urging member housings formed on the driving gear at regular intervals in the circumferential direction thereof, the urging members being three cylindrical compression springs.
A fifth invention provides two-wheel drive and four-wheel drive change-over apparatus having a first change-over shaft for switching two-wheel drive/four-wheel drive and a second change-over shaft for changing speeds of four wheels, the first and second change-over shafts being arranged in parallel with each other in a transfer and movable in axial directions thereof, cams held on the first and second change-over shafts for driving the first and the second change-over shafts respectively, and an actuator adapted to be driven rotationally to predetermined stopping positions respectively in accordance with a mode changed by a switching operation of a mode change-over switch, and drive each cam and thereby move the change-over shafts selectively in the axial directions thereof at predetermined strokes, wherein the actuator includes: a motor adapted to be rotated forward or backward by a current supplied thereto, a driving gear meshed with a worm formed on a shaft of the motor, an output shaft connected to the driving gear, a pair of cam followers adapted to be turned by a rotation of the output shaft, and engaged with each of the cams and drive the same, urging members held in urging member housings formed at predetermined intervals along a circle which is the same as an outer circumference of the driving gear, a rotation retaining plate supported on the output shaft so that the rotation retaining plate cannot be rotated relatively thereto, a plurality of pressing parts each of which is formed so as to project from the rotation retaining plate, and each of which is capable of pressing either one of both end portions of a corresponding urging member, slits formed in the portions of the driving gear which are among the urging member housings so as to prevent the driving gear and pressing parts from interfering with each other, a first actuator case in which the driving gear, rotation retaining plate and output shaft are housed, and a second actuator case fixed to the first actuator case, supporting the change-over shafts so that the change-over shafts can be moved freely in the axial direction, and housing the cams therein, a rotation of the driving gear being transmitted to the output shaft via each urging member and rotation retaining plate, either one of both end portions of each urging member being pressed by a corresponding pressing part of the rotation retaining plate when the rotation of the driving gear is continued after the output shaft is locked and stopped in the intermediate position of the rotation thereof.
A sixth invention provides a two-wheel drive and four-wheel drive change-over apparatus which is in accordance with that of the fifth invention, in which the plural urging member housings formed on the driving gear are three arcuate urging member housings formed on the driving gear at regular intervals in the circumferential direction thereof, the urging members being three cylindrical compression springs.